Spark plug



April 22, 1941.

' Filed Jan. 17, 1940 M TOR I BY W MTORNEY Patented Apr. 22, 1941Bernard Hopps,

Rugby, England, assignor to Baker & Company, Inc., 'a corporation of NewJersey Application January 17, 1940, Serial-No. 314,228 In Great BritainJanuary 19, 1939 7 Claims.

This invention relates in general to spark plugs and is directedparticularly to an improvement in precious metal sparking plugelectrodes. Sparking plug electrodes of plainum have been usedheretofore in various applications such as in gasoline engines. I

It is one object of my invention to produce a sparking plug electrodewhich shall consist primarily of platinum, but which shall have greaterresistance to attack and erosion than platinum or alloys of platinumused heretofore.

It is another object of my invention to produce a sparking plugelectrode which shall be not only more resistant to chemical attack butalso of greater rigidity at high temperatures and which shall have alower voltage gap, than electrodes of platinum or alloys of platinumheretofore known.

A further object of my invention is to produce spark plugs particularlyfor use in airplane gasoline engines, which shall have electrodes thatpossess great resistance to chemical attack, great resistance tooxidation, great rigidity, low electrical resistivity, and which willrequire lower voltage to produce a spark across a given gap than otherelectrodes.

I have found that these and other beneficial objects can be simply andeffectively obtained by alloying rhodium with platinum. Sparking plugelectrodes of platinum having rhodium alloyed thereto are extremelyresistant to chemical attack and erosion and more so than electrodes ofplatinum or platinum alloys now in use. Such electrodes, according to myinvention, have great rigidity and maintain great rigidity at hightemperatures and do not bend or distort;

they resist oxidation and erosion and have low electrical resistivity.v

Such electrodes furthermore provide a low voltage gap, 1. e. require alower voltage to produce a spark across a given gap than otherelectrodes.

According to my invention the sparking plug electrode consists ofplatinum with which rhodium has been alloyed. The alloy should alwaysconsist of a content of platinum relatively greater than the content ofrhodium, the alloy comprising for instance not less than fifty percent(50%) platinum and, preferably, not less than seventy percent (70%)platinum. The alloy may also have a small content of other metals of theplatinum group, i. e. osmium, ruthenium,

iridium or palladium. While the alloy of my' sparking electrodes thusconsists of a major proportion of platinum and a minor proportion ofrhod um. t m y also contain a small quantity of a metal or metals of thegroup comprising osmium, ruthenium, iridium and palladium. In particularmy alloys will contain not in excess of about thirty percent (30%)rhodium, even small quantities such as two percent (2%) to five percent(5%) being sufflcient to produce sparking plug electrodes having thedesired improved properties; and the alloys may contain for instance upto about ten percent (10%) ofat least one of the metals'osmium,ruthenium, iridium and palladium, alloys containing even as small amountas one percent (1%) of such metals being accompanied by considerableadvantages, particularly where the rhodium content does not exceed abouttwenty percent (20%). When such other metals are present the platinumcontent should still be in excess of fifty percent and preferably inexcess of sixty percent or seventy percent Platinum alloyed with tenpercent (10%) rhodium will have a Brinellhardness of 165 when hard andof 90 when fully annealed at about 1000 C., a hardness which can beincreased still further by the additional alloying therewith of at leastone metal of the group comprising osmium, ruthenium, iridium andpalladium. The same alloy consisting of ten percent (10%) rhodium, theremainder being platinum, has a melting point of 1820 C. and comparesfavorably with a melting point of 1810 C. for an alloy of platinum andtwenty percent (20%) iridium and exceeds the melting point of 1780 C.for an alloy of platinum and ten percent 10%) iridium. The electricalresistivity at 1000 C. in terms of ohms/mil. ft. is 280 for an alloy ofninety percent (90%) platinum and ten percent (10%) rhodium, whereas itis 315 for an alloy of ninety percent (90%) platinum and ten percent(10%) iridium, and 355 for an alloy of eighty percent platinum andtwenty percent (20%) iridium.

Sparking plug electrodes made of platinum alloyed with ten percent (10%)rhodium and, other combinations within the scope of my invention andused in actual practice in airplane gasoline engines have shown aconsistently better performance than electrodes of platinum or alloys ofplatinum containing iridium, and the like alloys. They have been founduseful even in connection with doped gasolines. Such electrodes maintaintheir high strength and rigidity extremely well and have a lowelectrical resistivity. They require a lower voltage to produce a sparkacross a given gap than other electrodes, thus having a low voltage gap.

For the purpose of illustrating the invention, I have shown in theaccompanying drawing an. elementary spark plug embodying electrodesconstructed in accordance with the invention.

The figure in the drawing is a transverse vertical sectional viewthrough a spark plug.

The spark plug is shown as comprising a metallic body or casing I havinga socket 2 in which is mounted an electrical insulating core 3 that isheld in position in the body by a cap nut l. A central electrode 5 ismounted in and extends longitudinally of the core 3 with one end 6projecting from the core for attachment in an electric circuit, and theother end I projecting from the opposite end of the core and body I inspaced relation to an outer electrode 8 which is mounted on andelectrically connected to the body or casing I, whereby a spark gap isprovided between the two electrodes.

In accordance with the invention, at least one, and preferably both, ofthe electrodes are formed of an alloy comprising rhodium and platinum asherein-before described.

Having thus described my invention, what I claim is:

1. A sparking plug electrode consisting of rhodium alloyed withplatinum, the platinum constituting at least about fifty percent (50%)of the alloy.

2. A sparking plug electrode consisting of an alloy of rhodium andplatinum in which the rhodium content does not exceed about fortypercent and the platinum content is not below about seventy percent(70%).. g

3. A sparking plug electrode comprising an alloy containing rhodium andplatinum and including not in excess of about thirty percent (30%)rhodium, not less than fifty percent,

(%) platinum and not in excess of about ten percent (10%) of at leastone metal of the group comprising osmium, ruthenium, iridium andpailadium.

4. A sparking plug electrode consisting of an alloy of rhodium andplatinum containing up to twenty percent (20%) rhodium, the remainderbeing platinum.

5. A spark plug comprising a pair of electrodes electrically insulatedfrom each other, wherein at least one electrode consists of an alloy ofrhodium and platinum in which platinum constitutes at least fiftypercent (50%) of the alloy.

6. A spark plug having an electrode comprising an alloy of rhodium andplatinum wherein the rhodium content constitutes up to twenty percent(20%) of the alloy and the remainder is platinum.

7. A spark plug comprising a pair of electrodes electrically insulatedfrom each other and each formed of an alloy containing rhodium and atleast fifty percent (50%) of platinum.

BERNARD HOPPS.

